Copper bonding compatible bond pad structure and method

ABSTRACT

A copper bonding compatible bond pad structure and associated method is disclosed. The device bond pad structure includes a buffering structure formed of regions of interconnect metal and regions of non-conductive passivation material, the buffering structure providing buffering of underlying layers and structures of the device.

The present application claims priority to, and is continuation of U.S.patent application Ser. No. 12/541,881 filed on Aug. 13, 2009 now U.S.Pat. No. 8,148,256, which is a divisional patent application of, U.S.patent application Ser. No. 11/444,977 filed on 31 May 2006 now U.S.Pat. No. 7,598,620 and having Franois Hebert and Anup Bhalla listed asinventors. The aforementioned patent applications are incorporated byreference herein.

BACKGROUND OF THE INVENTION

The present invention generally relates to bond pad structures andmethods of bonding semiconductor devices to substrates and moreparticularly to a copper bonding compatible bond pad structure and amethod of bonding copper bonding wires to a semiconductor device withoutdamaging device package layers and underlying device structures.

Conventional bonding methods utilize either Al or Au bonding wires toconnect the semiconductor device to a substrate such as a leadframe. Alsuffers the disadvantage of having high resistance while Au isincreasingly expensive.

Cu bonding wires have been considered an inexpensive alternative to Aland Au bonding wires. Cu is inexpensive, readily available, and has lowresistance. As such, fewer Cu bonding wires are generally required.However, Cu bonding wires are harder than either Al or Au bonding wiresand their use presents challenges not satisfactorily overcome by theprior art.

As Cu and Cu alloys are harder than conventional bonding wires, bondingusing Cu and Cu alloy bonding wires may result in damage to thesemiconductor device or to package layers forming a device bond pad.With reference to FIG. 1, an exemplary prior art semiconductor device100 includes a substrate 110 having a semiconductor device (not shown)formed therein. Substrate 110 may be formed of Si and the semiconductordevice may include a power MOSFET. A TiNi barrier metal layer 120 isdisposed under an Al, AlCu or AlSiCu electrode metal layer 130. A bondpad 140 may be formed by patterning a passivation layer 150 formed ofoxynitride or silicon rich oxynitride. Bond pad 140 may include a MOSFETsource bond pad.

A Cu bond wire 200 is shown in FIG. 2 and FIG. 3 bonded to the bond pad140. As shown in FIG. 3, the Cu bond wire 200 has penetrated theelectrode metal layer 130 and partially penetrated the barrier metallayer 120. Damage to the barrier metal layer 120 can result in junctionleakage and/or device failure over time. In an extreme case (not shown),the Cu bond wire 200 may completely penetrate the barrier metal layer120 and damage the semiconductor device.

To address this problem, prior art techniques use a very thick electrodemetal layer 130. Typical thicknesses are much greater than 3 micron andtypically 6 microns. This technique disadvantageously increases materialand manufacturing costs making the patterning of fine lines in thedevice interconnects very difficult.

There is therefore a need in the art for a copper bonding compatiblebond pad structure and associated method that does not damage thebarrier metal layer or underlying device structures. There is a furtherneed in the art for a bond pad structure and associated method thatachieves low contact resistance. There is also a need in the art for abond pad structure and associated method that can be achieved at noadditional processing cost.

SUMMARY OF THE INVENTION

The present invention overcomes the limitations of the prior art byproviding a copper bonding compatible bond pad structure and associatedmethod wherein the Cu bonding wire is buffered from the barrier metallayer. This buffering is accomplished by a buffering structure formed inthe bond pad. The buffering structure includes regions of electrodemetal and regions of dielectric passivation material which serve tobuffer the Cu bonding wire and protect the barrier metal layer. Thebuffering structure is formed by patterning and etching the dielectricpassivation layer when forming the bond pad.

In accordance with one aspect of the invention, a device bond padincludes a buffering structure formed of regions of interconnect metaland regions of non-conductive passivation material, the bufferingstructure providing buffering of underlying layers and structures of thedevice.

In accordance with yet another aspect of the invention, a method offorming a Cu bonding compatible bond pad structure includes the steps of(a) determining a buffering structure pattern, (b) patterning thebuffering structure pattern on a dielectric passivation layer, and (c)processing the buffering structure pattern to create a bufferingstructure in the bond pad. Cu bonding compatible bond pad structurecomprising:

In accordance with still another aspect of the invention, a Cu bondingcompatible bond pad structure includes a buffering structure formed ofregions of interconnect metal and regions of non-conductive passivationmaterial, wherein the regions of non-conductive passivation material areformed from a dielectric passivation layer and the regions ofinterconnect metal are formed on an electrode interconnect metal layerunderlying the dielectric passivation layer

There has been outlined, rather broadly, the more important features ofthe invention in order that the detailed description thereof thatfollows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described below andwhich will form the subject matter of the claims appended herein.

In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of design and to thearrangement of components or process steps set forth in the followingdescription or illustrated in the drawings. The invention is capable ofother embodiments and of being practiced and carried out in variousways. Also, it is to be understood that the phraseology and terminologyemployed herein, as well as the abstract, are for the purpose ofdescription and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conceptionupon which this disclosure is based may readily be utilized as a basisfor the designing of other methods and systems for carrying out theseveral purposes of the present invention. It is important, therefore,that the claims be regarded as including such equivalent methods andsystems insofar as they do not depart from the spirit and scope of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a prior art bond pad;

FIG. 2 is a top view of a Cu bonding wire attached to the bond pad ofFIG. 1;

FIG. 3 is a cross sectional view of the Cu bonding wire shown in FIG. 2;

FIG. 4 is a top view of a buffering structure in accordance with theinvention;

FIG. 5 is a cross sectional view of the buffering structure of FIG. 4 inaccordance with the invention;

FIG. 6 is a cross sectional view of a Cu bonding wire attached to thebuffering structure of FIG. 4 in accordance with the invention; and

FIG. 7 is a flow chart of a method of forming a buffering structure inaccordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best modes of carrying outthe invention. The description is not to be taken in a limiting sense,but is made merely for the purpose of illustrating the generalprinciples of the invention, since the scope of the invention is bestdefined by the appended claims.

The present invention generally provides a Cu bonding compatible bondpad structure that buffers bonding damage. A buffering structure isformed in the bond pad when the bond pad is patterned on the dielectricpassivation layer deposited and formed on a semiconductor devicesurface. The buffering structure may include regions of electrodeinterconnect metal and regions of non-conductive passivation material,the passivation material being patterned in the shape of dots, squares,rectangles, stripes, grid structures, zigzags, chevrons, waves or anyother shape or configuration.

With reference to FIG. 4, FIG. 5, and FIG. 6, a Cu bonding compatiblebond pad structure 400 includes a buffering structure 410 formed in thebond pad structure 400. The buffering structure 410 includes regions 415of exposed electrode metal of an electrode metal layer 420 and regions417 of non-conductive passivation material of a passivation layer 460.Regions 417 may include dots, squares, rectangles, stripes, gridstructures, zigzags, chevrons, waves or any other shape orconfiguration. The electrode metal layer 420 may comprise a layer ofAlCu or AlSiCu. The electrode metal layer 420 is formed over a TiNibarrier metal layer 430.

Upon bonding of a Cu bonding wire 450 to the bond pad structure 400, theAlCu or AlSiCu of the electrode metal layer 420 will be squeezed by thepressure of the Cu bonding wire 450 and flow in a plurality ofdirections within the buffering structure 410 around, under and over theregions 417 of the patterned passivation material, depending upon theconfiguration of the regions 415 and 417. Some of the regions 417 may bepushed into the AlCu or AlSiCu of the electrode metal layer 420 toprovide a buffer or cushion to the Cu bonding wire 450 and keep the Cubonding wire 450 away from the barrier metal layer 430 and asemiconductor device 440.

The pattern and width and spacing of the regions 417 of the patternedpassivation material and of the regions 415 of exposed electrode metalcan be optimized depending upon the metal of the bonding wire and thebonding conditions. Furthermore, an aspect ratio or pattern density andrelated dimensions and shapes of the regions 415 and 417 can beoptimized to minimize the impact on the contact resistance of the bond.More regions 417 of the patterned passivation material relative to theregions 415 of exposed electrode metal (a higher aspect ratio) mayprovide for greater barrier layer and underlying device structureprotection. Less regions 417 relative to the regions 415 (a lower aspectratio) may provide for lower contact resistance. Additionally, groupingsof regions 415 and 417 can also be utilized in order to limit any stressand movement on the passivation layer 460.

A method of forming a Cu bonding compatible bond pad structure inaccordance with the invention may include patterning the bufferingstructure 410 in the bond pad 400. With reference to FIG. 7, a methodgenerally designated 700 includes a step 720 in which the pattern of abuffering structure is determined. The buffering structure pattern mayprovide for an optimized aspect ratio. The buffering structure patternis then patterned onto a dielectric passivation layer in a step 730.Finally, the pattern is etched in a step 740 to create the bufferingstructure. The buffering structure includes regions of exposed electrodemetal of an electrode metal layer and regions of non-conductivepassivation material.

The present invention advantageously provides for a Cu bondingcompatible bond pad structure that buffers Cu bonding damage to thebarrier metal layer and the semiconductor device. The bond pad structurecan be obtained at no additional processing cost by patterning thepassivation layer to create the buffering structure. The bufferingstructure provides for low contact resistance.

It should be understood, of course, that the foregoing relates topreferred embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

We claim:
 1. A method of forming a Cu bonding compatible bond padstructure comprising the steps of: depositing passivation material uponsaid bond pad structure; patterning a buffering structure pattern onsaid passivation material to provide a plurality of spaced-apart regionsof said passivation material spaced-apart along a first direction,defining a plurality of hiatuses, portions of said bond pad structure insuperimposition with said hiatuses being exposed and spaced-apart from acrown surface of said regions along a second direction, extendingtransversely to said first direction; etching said buffering structurepattern to create said Cu bonding compatible bond pad structure; andattaching a bond wire to a top of said buffer structure pattern pushinga portion of the buffer structure pattern downward for the bond wireconnecting to a metal layer underneath the buffer structure pattern.